The present invention is generally directed to USB device redirection in a virtual desktop infrastructure (VDI) environment. USB device redirection generally refers to making a USB device that is connected to a client accessible within a virtual desktop as if the USB device had been physically connected to the virtual desktop. In other words, when USB device redirection is implemented, a user can connect a USB device to his or her client terminal and the USB device will function as if it had been connected to the server.
FIGS. 1, 2A and 2B and the following description will provide a general overview of how USB device redirection can be implemented in accordance with some embodiments of the present invention. In FIG. 1, a computing system 100 is depicted as including a number of client terminals 102a-102n (referenced generally herein as client(s) 102) in communication with a server 104 via a network 106. Server 104 can be configured to support a remote session (e.g., a remote desktop session) wherein a user at a client 102 can remotely access applications and data at the server 104 from the client 102. Such a connection may be established using any of several well-known techniques such as the Remote Desktop Protocol (RDP) and the Citrix® Independent Computing Architecture (ICA).
Client terminal 102 may represent a computer, a mobile phone (e.g., smart phone), a laptop computer, a thin client terminal, a personal digital assistant (PDA), a portable computing terminal, or a suitable terminal or device with a processor. Server 104 may represent a computer, a laptop computer, a computing terminal, a virtual machine (e.g., VMware® Virtual Machine), a desktop session (e.g., Microsoft Terminal Server), a published application (e.g., Microsoft Terminal Server) or a suitable terminal with a processor.
Client 102 may initiate a remote session with server 104 by sending a request for remote access and credentials (e.g., login name and password) to server 104. If server 104 accepts the credentials from client 102, then server 104 may establish a remote session, which allows a user at client 102 to access applications and data at server 104. During the remote session, server 104 sends display data to client 102 over network 106, which may include display data of a desktop and/or one or more applications running on server 104. The desktop may include, for example, icons corresponding to different applications that can be launched on server 104. The display data allows client 102 to locally display the desktop and/or applications running on server 104.
During the remote session, client 102 may send user commands (e.g., inputted via a mouse or keyboard at client 102) to server 104 over network 106. Server 104 may process the user commands from client 102 similar to user commands received from an input device that is local to server 104. For example, if the user commands include mouse movements, then server 104 may move a pointer on the desktop running on server 104 accordingly. When the display data of the desktop and/or application changes in response to the user commands, server 104 sends the updated display data to client 102. Client 102 locally displays the updated display data so that the user at client 102 can view changes at server 104 in response to the user commands. Together, these aspects allow the user at client 102 to locally view and input commands to the desktop and/or application that is running remotely on server 104. From the perspective of the client side, the desktop running on server 104 may represent a virtual desktop environment.
FIG. 2A is a block diagram of a local device virtualization system 200 in accordance with embodiments of the present invention. System 200 may include client 102 in communication with server 104 over network 106 as illustrated in FIG. 1. Client 102 may include a proxy 210, a stub driver 220, and a bus driver 230. Client 102 can be connected to a device 240, as shown in FIG. 2A. Server 104 may include an agent 250 and a virtual bus driver 260.
In accordance with USB device redirection techniques, while device 240 is not locally or physically connected to server 104 and is remote to server 104, device 240 appears to server 104 as if it is locally connected to server 104, as discussed further below. Thus, device 240 appears to server 104 as a virtual device 290.
By way of illustration and not limitation, device 240 may be any type of USB device including a machine-readable storage medium (e.g., flash storage device), a printer, a scanner, a camera, a facsimile machine, a phone, an audio device (e.g., a headset), a video device (e.g., a camera), a peripheral device, or other suitable device that can be connected to client 102. Device 240 may be an external device (i.e., external to client 102) or an internal device (i.e., internal to client 102).
Bus driver 230 can be configured to allow the operating system and programs of client 102 to interact with device 240. In one aspect, when device 240 is connected to client 102 (e.g., plugged into a port of client 102), bus driver 230 may detect the presence of device 240 and read information regarding device 240 (“device information”) from device 240. The device information may include features, characteristics and other information specific to device 240 such as a device descriptor (e.g., product ID, vendor ID and/or other information), a configuration descriptor, an interface descriptor, an endpoint descriptor and/or a string descriptor. Bus driver 230 may communicate with device 240 through a computer bus or other wired or wireless communications interface.
In accordance with USB device redirection techniques, device 240 may be accessed from server 104 as if the device were connected locally to server 240. Device 240 may be accessed from server 104 when client 102 is connected to server 104 through a user session running on server 104. For example, device 240 may be accessible from the desktop running on server 104 (i.e., virtual desktop environment). To enable this, bus driver 230 may be configured to load stub driver 220 as the default driver for device 240. Stub driver 220 may be configured to report the presence of device 240 to proxy 210 and to provide the device information (e.g., device descriptor) to proxy 210. Proxy 210 may be configured to report the presence of device 240, along with the device information, to agent 250 of server 104 over network 106. Thus, stub driver 220 redirects device 240 to server 104 via proxy 210.
Agent 250 may be configured to receive the report from proxy 210 that device 240 is connected to client 102 and the device information. Agent 250 may further be configured to associate with the report from proxy 210 one or more identifiers for client 102 and/or for a user session through which client 102 is connected to server 104, such as a session number or a session locally unique identifier (LUID). Agent 250 can provide notification of device 240, along with the device information, to virtual bus driver 260. Virtual bus driver 260 (which may be a TCX USB bus driver, or any other bus driver) may be configured to create and store in memory a record corresponding to device 240, the record including at least part of the device information and session identifiers received from agent 250. Virtual bus driver 260 may be configured to report to operating system 170 of server 104 that device 240 is connected and to provide the device information to the operating system. This allows the operating system of server 104 to recognize the presence of device 240 even though device 240 is connected to client 102.
The operating system of server 104 may use the device information to find and load one or more appropriate device drivers for device 240 at server 104. Each driver may have an associated device object (object(s) 281a, 281b, . . . , 281n, referred to generally as device object(s) 281), as illustratively shown in FIG. 2A. A device object 281 is a software implementation of a real device 240 or a virtualized (or conceptual) device 290. Different device objects 281 layer over each other to provide the complete functionality. The different device objects 281 are associated with different device drivers (driver(s) 282a, 282b, . . . 282n, referred to generally as device driver(s) 282). In an example, a device 240 such as a USB flash drive may have associated device objects including objects corresponding to a USB driver, a storage driver, a volume manager driver, and a file system driver for the device. The device objects 281 corresponding to a same device 240 form a layered device stack 280 for device 240. For example, for a USB device, a USB bus driver will create a device object 281a stating that a new device has been plugged in. Next, a plug-and-play (PNP) component of the operating system will search for and load the best driver for device 240, which will create another device object 281b that is layered over the previous device object 281a. The layering of device objects 281 will create device stack 280.
Device objects 281 may be stored in a memory of the server 104 associated with virtual bus driver 260. In particular, device objects 281 and resulting device stack 280 may be stored in random-access memory of server 104. Different devices 240/290 can have device stacks having different device objects and different numbers of device objects. The device stack may be ordered, such that lower level device objects (corresponding to lower level device drivers) have lower numbers than higher level device objects (corresponding to higher level device drivers). The device stack may be traversed downwards by traversing the stack from higher level objects to lower level objects. For example, in the case of an illustrative device stack 280 corresponding to a USB flash drive, the ordered device stack may be traversed downwards from a high-level file system driver device object, to a volume manager driver device object, to a storage driver device object, to a USB driver device object, and finally to a low-level virtual bus driver device object. Different device stacks 280 can be layered over each other to provide the functionality of the devices 240/290 inside devices, like USB Headsets, or USB pen drives. A USB pen drive, for example, can create a USB device stack first, over which it can create a storage device stack, where each of the device stacks have two or more device objects.
Once one or more device object(s) 281 are loaded by operating system 170 of server 104, each device object 281 can create a symbolic link (also referred to as a “device interface”) to device object 281 and associated device driver 282. The symbolic link is used by applications running on server 104 to access device object 281 and device 240/290. The symbolic link can be created by a call to a function such as IoCreateSymbolicLink( ) including such arguments as a name for the symbolic link, and a name of device object 281 or associated device 240. In one example, for example, a symbolic link to a USB flash drive device 240 is created by a call from a device object 281 for device 240 to the function IoCreateSymbolicLink( ) including arguments “\\GLOBAL??\C:” (i.e., the name for the symbolic link) and “\Device\HarddiskVolume1” (i.e., a name of the device object).
The creation of a symbolic link results in an entry being created in an object manager namespace (OMN) of operating system 170. The OMN stores information on symbolic links created for and used by operating system 170, including symbolic links for devices 240, virtualized devices 290, and applications 270 running on server 104.
As a result of the symbolic link creation process, a symbolic link to device 240 is enumerated in the OMN of server 104. Once the presence of device 240 is reported to operating system 170 of server 104, device 240 may be accessible from a user session (and associated desktop) running on server 104 (i.e., virtual desktop environment). For example, device 240 may appear as an icon on the virtual desktop environment and/or may be accessed by applications running on server 104.
An application 270 running on server 104 may access device 240 by sending a transaction request including the symbolic link for device 240 to operating system 170. Operating system 170 may consult the Object Manager Namespace to retrieve an address or other identifier for the device itself 240 or for a device object 281 associated with device 240. Using the retrieved address or identifier, operating system 170 forwards the transaction request for device 240 either directly, through a device object 281 of device stack 280, and/or through virtual bus driver 260. Virtual bus driver 260 may direct the transaction request to agent 250, which sends the transaction request to proxy 210 over network 106. Proxy 210 receives the transaction request from agent 250, and directs the received transaction request to stub driver 220. Stub driver 220 then directs the transaction request to device 240 through bus driver 230.
Bus driver 230 receives the result of the transaction request from device 240 and sends the result of the transaction request to stub driver 220. Stub driver 220 directs the result of the transaction request to proxy 210, which sends the result of the transaction request to agent 250 over network 106. Agent 250 directs the result of the transaction request to virtual bus driver 260. Virtual bus driver 260 then directs the result of the transaction request to application 270 either directly or through a device object 281 of device stack 280.
Thus, virtual bus driver 260 may receive transaction requests for device 240 from application 270 and send results of the transaction requests back to application 270 (either directly or through a device object 281 of device stack 280). As such, application 270 may interact with virtual bus driver 260 in the same way as with a bus driver for a device that is connected locally to server 104. Virtual bus driver 260 may hide the fact that it sends transaction requests to agent 250 and receives the results of the transaction requests from agent 250 instead of a device that is connected locally to server 104. As a result, device 240 connected to client 102 may appear to application 270 as if the physical device 240 is connected locally to server 104.
The Object Manager Namespace (OMN) stores information on symbolic links created for use by operating system 170, including symbolic links for devices and for applications running on server 104. The Object Manager Namespace generally includes several different namespaces for storing symbolic link information for applications and devices. For example, the Object Manager Namespace can include namespaces such as: a “Global” namespace used to store symbolic link information for devices and applications that are shared by all user sessions running on server 104; various “Local” namespaces, each associated with a user session running on server 104, used to store information for applications used by (and restricted to) the associated user session; and a “Device” namespace used to store device object names of devices and virtual devices accessible by server 104. A “Global” namespace may be referred to as a global namespace. A “Local” namespace may be referred to as a local namespace. A “Device” namespace may be referred to as a device namespace.
As described herein, symbolic links can be stored in a global namespace or a local namespace. Symbolic links stored in a global namespace may be available to the entire system (i.e., to all user sessions running on server 104), while symbolic links stored in a local namespace may only be seen and accessed by the session for which they are created. For example, “\\GLOBAL??\c:” may be a symbolic link stored in a global namespace. “\Device\HarddiskVolume1” may be a device object name stored in a device namespace. A symbolic link “\\GLOBAL??\c:” may be pointing to a device object having a device object name of “\Device\HarddiskVolume1”. Because “c:” is a symbolic link in the global namespace directory, such a symbolic link may be accessed by the entire system, including all the users logged in through their respective user sessions. A user application can open “\\GLOBAL??\c:” or just “c:” to access the actual device.
In certain operating systems, such as the Windows operating system, the creation of the symbolic link for a device 240 results in an entry being created in a Global namespace of the Object Manager Namespace. Because the symbolic link is created in the Global namespace, the symbolic link can be accessed from any user session running on server 104. As a result, the device 240 associated with the symbolic link can be accessed from any user session on server 104, and/or from any client terminal having an active user session on server 104.
FIG. 2B illustratively shows a block diagram of a computer system 100 providing local device virtualization. As previously described in relation to FIG. 1, system 100 includes client terminals 102a-102n communicating through network 106 with server 104. As described in relation to FIG. 2A above, each device 240a, 240b can be virtualized on server 104 to provide access to the device from a user session on server 104 through a corresponding virtual device 290a, 290b. For example, when device 240a is connected to client terminal 102a, drivers for device 240a may be loaded in operating system 170 of server 104, device 240a may be virtualized on server 104 as virtual device 290a, and a symbolic link to the device 240a may be created in the Object Manager Namespace of operating system 170. Once the symbolic link is created, a user of client terminal 102a may be able to access device 240a through a user session on server 104. Similarly, when device 240b is connected to client terminal 102b, a symbolic link to the device 240b may be created in the Object Manager Namespace of operating system 170 of server 104. Once the symbolic link is created, a user of client terminal 102b may be able to access device 240b through a user session on server 104.
The symbolic links to the devices 240a, 240b are created in a Global namespace of the Object Manager Namespace of operating system 170. As a result, the symbolic links and associated devices can be accessed from and used by any user session running on server 104. For example, as illustratively shown in FIG. 2B, a user of client terminal 102a having a user session on server 104 may access both device 240a as well as virtual device 240b′ from the user session. Similarly, a user of client terminal 102b having a user session on server 104 may access both device 240b as well as virtual device 240a′ from the user session. Finally, a user of client terminal 102c having a user session on server 104 may access both virtual device 240a′ and 240b′ from the user session.
Hence, the device virtualization described in relation to FIGS. 2A and 2B provides unrestricted access to devices 240 connected locally to client terminals 102 from any user session on server 104. As such, a redirected device becomes a local device to the server and can be accessed by all the users' sessions connected to that server. For example a printer or a mass storage device, when redirected by one user connected through a session on the server, will show up as a local device and all the users can read/write the mass storage device and print using the printer.
While the unrestricted access enables users of client terminals 102 to share access to and use of devices 240, the device virtualization does not permit a user to restrict access to a device 240. In this respect, the unrestricted device virtualization does not permit secure or private access to device 240. The device virtualization thus presents security and privacy concerns, as a device 240 may be accessed or used by any number of unauthorized users having user sessions on server 104. In order to address these security and privacy concerns, a device virtualization system may require that a device connected through a session only be accessible in that session.
FIG. 3 is a block diagram of a system 300 that can be employed to enforce session level restrictions to limit access to a redirected USB device. System 300 may include a client 102 in communication with a server 304 over network 106 such as is depicted in FIG. 1. Client 102, including proxy 210, stub driver 220, bus driver 230, and one or more optional device(s) 240, is substantially similar to the client 102 shown in and described in relation to FIG. 2A. Server 304 includes agent 250, virtual bus driver 260, device stack 280 including device objects 281a, 281b, . . . , 281n, device drivers 282a, 282b, . . . , 282n, operating system 170, application 270, and one or more optional virtualized device(s) 290, which function substantially similarly to the corresponding elements of server 104 of FIG. 2A.
Server 304 additionally includes a Device Access Restriction object (DAR object) 180 at the top of device stack 280. A Device Access Restriction driver (DAR driver) 182 creates and attaches DAR object 180 at the top of device stack 280. DAR driver 182 is registered with operating system 170 as the upper filter driver for all selected class(es) of devices for which access restriction is to be made. More particularly, DAR driver 182 associates itself with particular USB classes so that anytime a device in one of the particular classes is connected/redirected, operating system 170 will invoke DAR driver 182's AddDevice routine. When invoked, and possibly based on a determination that the device is in a class that should be session isolated, DAR driver 182 creates DAR object 180 and attaches the DAR object at the top of device stack 280.
Server 304 functions substantially similarly to server 104 in terms of loading drivers and device objects for device 240 on server 304. However, as discussed above, DAR driver 182 is registered as the upper filter driver for all the selected class(es) of devices for which access restriction is to be provided. For example, an image device class which includes webcams may be predetermined to be provided with access restriction. Such device classes may be predetermined by a user. When a device of the class, for which DAR driver 182 is registered, is plugged in, the DAR driver will be loaded and its add device routine may be called by operating system 170. For example, in cases where operating system 170 is a Windows system, a plug-and-play (PNP) component of the Windows Kernel will call an add device routine of DAR driver 182. Inside the add device routine, DAR driver 182 receives the physical device object of device stack 280 as an argument, which is used to verify that the device is a device redirected from client 102 using virtual bus driver 260. This verification is done by traversing device stack 280 downward until the bottom of the stack is reached or virtual bus driver 260 is found.
If virtual bus driver 260 is found in device stack 280, this signifies that the device is redirected from client 102 using the virtual bus driver. If the device is found to be redirected from client 102, DAR driver 182 creates DAR object 180 and attaches it (as the top object) onto device stack 280. However, if the bottom of device stack 280 is reached and virtual bus driver 260 is not found, this signifies that the device stack is not a device that is redirected from client 102, and thus no access restriction is to be provided. If the device is not found to be redirected, then DAR object 180 will not be attached on top of the device stack 280.
Since DAR object 180 is attached to the top of device stack 280, all requests for the redirected device are first received by DAR object 180. Thus, DAR object 180 can accept or reject the requests. For example, DAR object 180 can thus restrict a redirected device to be only accessible from the user session (e.g., a Microsoft windows terminal server session) it is redirected from. In some cases, this could be accomplished by blocking any I/O requests directed to device 240 that originate from any other user session. Alternatively, this could be accomplished by removing the symbolic link to device 240 from the global OMN and instead placing it in an local OMN specific to the user session which would not only block access to device 240 from other user sessions, but would prevent device 240 from being visible from the other user sessions.
The determination of whether to allow a particular USB device to be redirected and, if so, whether to apply session level restrictions is usually based on policy. For example, a policy may dictate that a particular user (or group) is allowed to redirect a printer but that any redirected printer should only be accessible from within the particular user's session. For the reasons presented above, these determinations must be made before a device is enumerated (i.e., before the process of detecting that a USB device has been connected, identifying the type of the connected USB device, and loading the appropriate drivers). As addressed above, in a redirection scenario, agent 250 will receive the device information from proxy 210 and provide this device information to virtual bus driver 260 which will then initiate the plug-and-play process. Agent 250 and/or virtual bus driver 260 may, based on policy, block the redirection of a USB device during this process (e.g., by failing to initiate the plug-and-play process if policy indicates that the particular class of USB devices should not be redirected). Similarly, DAR driver 182 must be registered for a particular USB class or USB classes in order to be invoked by the operating system during the plug-and-play process.
In short, the determination of whether to allow redirection and/or whether to require session isolation is based on the USB device descriptor. However, for many types of devices, the USB device descriptor is somewhat generic thereby preventing any type of granular control over which USB devices are allowed to be redirected and/or to which USB devices session level restrictions apply. As an example, scanners, biometric devices, and COM devices use a vendor specific class. Therefore, based only on the device descriptor, there is no way to determine whether a redirected device is a scanner, a biometric device, or a COM device. In short, for many types of USB devices, there is no unique USB device class that can be used to enable or disable redirection and/or session level restriction at the level of the device type. The only option would be to enable or disable these features for all USB devices that fall into a particular vendor specific class. For example, if it were desired to block biometric devices, this could only be accomplished by also blocking scanners and COM devices.